The present invention is in the field of polymer extruders and mixers for use in connection with providing high pressure polymer melts for injection moulding and extrusion and the like.
It is well known in the art to provide a polymer melt mixer in a heated extruder barrel, sometimes referred to as a stator, including a bore defining a cylindrical internal chamber in which a screw rotor is axially positioned for a rotation within and with respect to the cylindrical chamber. It is also conventional to have the upstream portion of the rotor comprise a driven rotary screw member for feeding the polymer components along the length of the rotor or barrel to a downstream portion which provides mixing of the melted components prior to injection of the polymer melt into a die or the like. The polymer melt injection is effected by moving the rotor in a downstream direction to force the viscous polymer melt constituents from the barrel out through an opening communicating with the interior of a die or the like. A device of the foregoing type is exemplified in prior U.S. Pat. No. 5,013,233.
It is extremely desirable that the polymer melt be thoroughly mixed following melting so as to achieve optimum uniformity of structure in the finished product produced by the injection molding operation. A number of different approaches have been suggested for achieving improved polymer melt mixing as evidenced by the following discussed prior art.
The Semmekrot U.S. Pat. Nos. 5,013,233 and 5,158,784 disclose a dimpled downstream rotor portion having cavities 22, 23 surrounded by a mixing ring or sleeve 9 having radial openings through which the polymer melt moves to and from the rotor dimples as it works its way from the upstream to the downstream end of the apparatus. Mixing occurs between cavities 22, 23 of the rotor and mixing ring 9 which is arranged for free rotation about the rotor of the Semmekorot device. The mixing ring or sleeve 9 is provided with an annular valve body 17 that coacts with a valve seat 18 on the rotor to prevent reverse flow of polymer melt in an upstream direction beyond a valve seat 18 during the injection process.
Another approach is revealed in Upmeier U.S. Pat. No. 4,541,982 which discloses a polymer melt extruder employing multiple fixedly positioned distributing disks positioned one behind the other in alignment with each other to effect a plurality of flow dividing mixing operations. The disks are arranged as stationary structures through which melt flow occurs in serial manner.
Sato U.S. Pat. No. 4,057,379 discloses an extruder having a driven screw type extruder screw 6 which forces melt material to be extruded through a driven rotating disk 12 having holes 14 into a stationary disk 16 having holes 26 and which is spaced from contact with the driven rotating disk.
West German DL 0155, 504 of Elektroger discloses a static mixing device for injection molding having plurality of discs 3 having flow through apertures 4 for producing turbulence and effecting mixing of polymer melt. Each of the discs is separated from the next adjacent disc by spacers to provide chambers between the discs. The discs and spacers are firmly clamped together so as to prevent them from rotating relative to each other.
British Patent No. 1,475,216 discloses a driven cylindrical rotor cooperating with a plurality of inner and outer profile rings for cooperation with the rotor for effecting mixing of polymer melt.
Applicant's earlier U.S. Pat. No. 4,779,989 discloses a transfer mixer assembly for use with an extruder screw employing a stator in which a rotor body 36 having grooves 37 and 42 is positioned for cooperation in effecting mixing.
While some of the known prior art devices have provided fairly satisfactory mixing results, there have remained a number of problems including inadequate mixing performance and the high cost of fabrication and maintenance due to the complexity of some of the devices.
Therefore, it is a primary object of the present invention to provide a new and improved mixer and/or mixer-intruder that provides enhanced mixing results, is economical to fabricate and maintain and is reliable and easy to use.